The polyphenylene ether resins are a family of engineering thermoplastics that are well known to the polymer art. These polymers may be made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof. By way of illustration, certain of the polyphenylene ethers are disclosed in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358. In the Hay patents, the polyphenylene ethers are prepared by an oxidative coupling reaction comprising passing an oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst. Other disclosures relating to processes for preparing polyphenylene ether resins, including graft copolymers of polyphenylene ethers with styrene type compounds, are found in Fox, U.S. Pat. No. 3,356,761; Sumitomo, U.K. Pat. No. 1,291,609; Bussink et al., U.S. Pat. No. 3,337,499; Blanchard et al., U.S. Pat. No. 3,219,626; Laakso et al., U.S. Pat. No. 3,342,892; Borman, U.S. Pat. No. 3,344,116; Hori et al., U.S. Pat. No. 3,384,619; Faurote et al., U.S. Pat. No. 3,440,217; and disclosures relating to metal-based catalysts which do not include amines, are known from patents such as Wieden et al., U.S. Pat. No. 3,442,885 (copper-amidines); Nakashio et al., U.S. Pat. No. 3,573,257 (metal-alcoholate or -phenolate); Kobayashi et al., U.S. Pat. No. 3,455,880 (cobalt chelates); and the like. In the Stamatoff patents, the polyphenylene ethers are produced by reacting the corresponding phenolate ion with an initiator, such as peroxy acid salt, an acid peroxide, a hypohalite, and the like, in the presence of a complexing agent. Disclosures relating to non-catalytic processes, such as oxidation with lead dioxide, silver oxide, etc., are described in Price et al., U.S. Pat. No. 3,382,212. Cizek, U.S. Pat. No. 3,383,435 discloses polyphenylene ether-styrene resin compositions. All of the above-mentioned disclosures are incorporated herein by reference.
In general, the mechanical or physical properties of polymers are very dependent upon molecular weight. With respect to polyphenylene ether resin compositions, it has been observed that, for example, the impact strength of a polyphenylene ether resin, as measured by Notched Izod impact, decreases in proportion to a decrease in the intrinsic viscosity and, correspondingly, the molecular weight of the polyphenylene ether resin. Conversely, a decrease in molecular weight results in improved processability.
It has generally been thought that the use of polyphenylene ether resins of relatively high molecular weight, i.e., 16,000 or greater, is essential if good impact strengths are to be obtained in the finished molded article. Such high molecular weight polyphenylene ether resins are characterized by having polymer chains of 130 units or more and intrinsic viscosities, as measured in chloroform at 30.degree. C., of at least about 0.4 dl/g or more.
It has now been surprisingly discovered that when a low molecular weight polyphenylene ether resin, i.e., having an intrinsic viscosity of less than 0.4 dl/g, preferably 0.33 dl/g, as measured in chloroform at 30.degree. C., is combined with an elastomeric block copolymer of a vinyl aromatic compound and a conjugated diene, and triphenyl phosphate as a plasticizer, the resulting composition possesses good impact strength. The results are unexpected in view of the strong belief in the prior art that low molecular weight polyphenylene ether resins should be avoided where high impact resistance is desired.
It is, therefore, a primary object of this invention to provide improved compositions that are based on polyphenylene ether resins, elastomeric block copolymers, and plasticizers.
Another object of this invention is to provide molding compositions and molded articles that are based on a polyphenylene ether resin and an elastomeric block copolymer and that have improved impact strength.
It is also an object of this invention to provide the above-described, improved molding compositions in reinforced and/or flame-retardant embodiments.